This invention relates to the detection of relatively weak signals against a background of noise, and typical uses are in the acoustic detection of aircraft, submarines, and land vehicles.
The invention is the subject of my currently copending Canadian application Ser. No. 115,983, filed June 18, 1971.
Two problems are involved in target detection, firstly the actual detection of the presence of a target, and secondly the location or direction-finding of that target. These two requirements are contradictory, since a narrow beam or sector of maximum sensitivity, which is desirable for direction-finding, leads to lack of sensitivity in neighboring directions. Thus an acoustic detection system using a narrow beam requires constant scanning by that beam, at a suitably low speed for detection to take place, if detection (as distinct from direction-finding) is important.
The present invention is directed to detection, rather than direction-finding, of a target.
Another of my copending Canadian patent applications No. 115,982, filed on June 18, 1971 describes a direction-finding system utilizing two microphones and a phase-difference detector which receives the outputs from the two microphones and combines those two outputs in a particular manner in a discriminator which enables the system to be used as a highly-directional device for direction-finding. It also describes an arrangement in which a greater number of pairs of microphones are combined in a similar manner. Such an arrangement provides a compact microphone system for a given narrowness of the beam produced.
It is possible to provide a beam of the same narrowness merely by using a sufficiently large array of microphones with their outputs combined in an additive manner, and for that given beam, the ability to detect a weak signal against background noise is better with the additive arrangement than with the more compact arrangement using discriminators.
An object of the present invention is to improve the detection of weak signals against a background of noise for any given number of signal-receiving transducers.